Workpiece shape and thickness control



1968 R. G. PLAISTED 0 WORKPIECE SHAPE AND THICKNESS CONTROL Filed April 29, 1966 4 Sheets-Sheet 1 FIG. I

A "2 I [b A b {-1 |2| I 1 c c FIG.2.

22s 2| w ROLL SCREW conggg low FORCE GAUGE MECHANISM A CONTROL I8 20 SHAPE CONTROL APPARATUS 24 L14 ,2 FORCE l DEVICE 1 FORCE CONTROL DEVICE H2 FIG. 3.

WITNESSES: INVENTDR Emu-QR? Gm Richard G.Plousted 7%M [BY-w ATTORNEY Oct. 8, 1968 PLAISTED 3,404,550

WORKPIECE SHAPE AND THICKNESS CONTROL v Filed April 29, 1966 4 Sheets-Sheet z HOUSING DEFORMATION I DUE TO RoLL FORCE LU Q g I EFCRMATION CuRvE IL D 50 OF METAL I O a:

s OUTPUT THICKNESS IMLUT THICKNESS STRIP THICKNESS FORCE 20 ON HOUSING.

b w 2C 71 (A) FORCE 2A8 0N m g I H9ysINe.2AB=(- A o I z I'- FORCE A EON sTRIP' l AREA WHERE I RoLL BENDING CoNTRoL NOT I USED I i OUTPUT L SARE; o THICKNESS INLUT I I TRAVEL-H THICKNESS STRIP THICKNESS FIG.5.

0d. 8, 1968 PLATSTED 3,404,550

WORKPIECE SHAPE AND THICKNESS CONTROL Filed April 29, 1966 4 Sheets-Sheet 4 92 6 REFERENCE O N ROLL RI HT ROLL FORCE FORCE e| 90 TRANSDUCER I AVERAGE ROLL FORCE ROLL FORCE THICKNESS LEFT ROLL CIRCUIT ERROR FORCE TRANSDUCER I00? SCREWDOWN CONTROL 2 (1,) I02 8 T n2 0 VOLTAGE U06 l 2 SOURCE n l I c l I l VOLTAGE l I soURcE QQ CONTROL SIGNAL SOURCE FIG. 7.

United States Patent 3,404,550 WORKPIECE SHAPE AND THICKNESS CONTROL Richard G. Plaisted, Williamsville, N.Y., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Apr. 29, 1966, Ser. No. 546,220 4 Claims. (Cl. 72-8) ABSTRACT OF THE DISCLOSURE The shape and the thickness of the workpiece strip delivered from a rolling mill are determined by a controlled bending of the work rolls such that any workpiece strip shape error is corrected in conjunction with obtaining a desired workpiece strip delivery thickness from the rolling mill.

The present invention relates in general to the control of workpiece strip thickness leaving a rolling mill, and more particularly to the control of the workpiece strip thickness through control of the roll shape in an effort to provide a desired delivery workpiece strip thickness and shape.-

It has been known in the prior art to grind the work rolls of a rolling mill to have a predetermined amount of crown, whereby the center portion of a roll has a larger diameter than the respective end portions, such that as the screwdown force is applied the attendant bending of the work rolls will result in a rolled strip having substantially parallel top and bottom surfaces or preferably having a small amount of camber or greater center thickness in the workpiece strip shape to be introduced to give a proper tracking of the workpiece strip through the rolling mill. It has also been known in the prior art to vary the shape of a rolled strip by a force applied between the work rolls, with hydarulic or other suitable force means, either to effect a bending of the rolls themselves or as an alternative to effect a positional adjustment of one or more of the work rolls in a direction substantially parallel to the strip movement.

It is an object of the present invention to provide improved workpiece shape and thickness control for a rolling mill that is operative such that the effects of undesired roll shape are better and more accurately corrected as well as improved delivery workpiece thickness control is realized.

It is a different object to provide improved workpiece shape and thickness control operative with the workpiece rolling mill to better control the delivery workpiece thickness relative to a desired workpiece thickness.

It is'an additional object of the present invention to provide an improved workpiece thickness control apparatus and a method for better controlling the work roll shape and to reduce the required changes of rolls in relation to the desired delivery work strip shape and thickness while permitting a given roll to be used for a greater variety of work strip parameters.

The present invention involves automatically regulating the delivery workpiece strip shape and thickness by controlling the shape or bending of the work roll to compensate for operational factors such as the width and thickness of the strip, the desired reduction, the alloy material, the temperature of the mill and of the workpiece and the operational speed of the mill by applying a bending force to the work rolls such that there results a correction in the measured shape error of the workpiece strip and then compensating any measured workpiece strip thickness. error in relation to the bending of the work rolls to provide a desired automatic strip thickness control operation.

Further objects and advantages of the present invention 3,404,550 Patented Oct. 8, 1968 will become more apparent from the following detailed description thereof with reference to the drawings in which:

FIGURE 1 is a cross-section showing of a typical roll member having a crown shape;

FIG. 2 illustrates the involved forces in accordance with the teachings of the present invention when a workpiece passes between the opposed rolls of a rolling mill;

FIG. 3 diagrammatically illustrates the operation of one embodiment of the present invention;

FIG. 4 is a curve illustrating the operation of the prior art apparatus in relation to roll force automatic strip thickness control;

FIG. 5 is a curve illustrating the different operational conditions present in a roll force strip thickness control system in accordance with the teachings of the present invention;

FIG. 6 is a diagrammatic showing of the control apparatus in accordance with one embodiment of the present invention; and

FIG. 7 is a schematic showing of a suitable control circuit arrangement for providing the compensation desired in accordance with the present invention.

It should be noted that the present invention is generally related to a copending patent application Ser. No. 417,323 filed Dec. 10, 1964, and now issued as U.S. Patent No. 3,318,124, by the same inventor and assigned to the same assignee.

In FIG. 1 there is shown a typical roll member for a rolling mill, which is ground to have a larger diameter at the center as compared to the ends of the roll. This is called a crowned roll and is utilized for more uniformly reducing the entering cross-section of the workpiece strip during a rolling operation.

In FIG. 2 there is generally shown an upper roll 10 and a lower roll 12 having screwdown mechanism forces B applied to the ends of the rolls. A resulting force A is in eifect applied to the center of the rolls 10 and 12 as shown due to the compression of the workpiece 14. When the workpiece 14 enters between the rolls 10 and 12 of the rolling mill, the separating forces due to the reduction of the workpiece 14 are distributed along the faces of the respective rolls 10 and 12. Equilibrium of metal reduction and roll deflection results in more deflection of the rolls 10 and 12, and consequently less reduction of the workpiece strip, at the center of the workpiece strip 14 as compared to the edges of the workpiece strip 14. The summation of all the distributed forces could be represented relative to the resultant roll bending, but by a composite force A shown in FIG. 2 at the distance b from the screw mechanism center line and screwdown force B. To restore the polls 10 and 12 to a shape such that their respective faces are substantially parallel throughout the width of the workpiece strip 14 would require a bending force C applied outside of and at some distance a from the center line of the screw mechanism. Since only the forces B and C can be conveniently measured, it is desirable to establish a predetermined relationship between forces B and C to provide the desired workpiece shape control and fiat roll surfaces under operational rolling conditions.

It is important that the delivery shape of rolled strip from hot mills and cold mills be controlled in reference to shape and flatness. The desired reduction in thickness should be across the whole width of the strip. The provision of a predetermined crown to the rolls is generally proper for one setting of rolling conditions only, and requires costly roll changes and a considerable supply of available and varied crowned rolls to enable any given rolling mill to properly roll a variety of workpiece sizes. The elfective crown of any given roll can be varied in accordance with the present teachings by a controlled bending. of the roll during the actual rolling mill operation, by applying suitable bending forces to the work rolls or to the backup rolls as' may be preferred. It is contemplated that a crown change of several thousandths of an inch can be provided in this way. This -will enable a given roll to be proper for a greater variety of workpiece dimensions Without the necessity of roll changes for that purpose. It should be additionally noted that thermally induced crown changes withinthe roll can be corrected by the roll bending teachings of the present invention. In the disclosure of the above referenced copending patent application, a system and method was described for maintaining a desired strip shape as the strip gauge or thicknes was varied and as the strip became harder. The teachings of the present invention include the modification required in the automatic gauge control system to Work with the automatic roll bending system to produce not only a workpiece strip with the required profile or shape but also having the proper thickness or gauge.

A reference to the involved forces shown in FIG. 2 will illustrate the forces on the work roll. The force A at a distance b from the center of the screw mechanism force B can be considered to be the equivalent force and the equivalent distance for any width workpiece strip being rolled. Any such strip being rolled will produce a torque equal to A b. In the roll bending system, the illustrated torque Ca is equal to the torque Ab. The values of A and B above are really incremental values when the roll itself is ground thicker in the center than at the ends. Only after this builtin contour has been utilized and .found to be inadequate, do the forces B and C start to be generated to oppose the force A beyond which the roll shape will not compensate to produce the desired shape or profile workpiece strip.

A plurality of equations can be very generally evolved in accordance with the force equilibrium conditions shown in FIG. 2 as follows:

In order that a change in force B will immediately result in proper proportional changes in the forces A/ 2 and C, if a hydraulic cylinder is used to provide force C the supply line should be automatically blocked by a solenoid controlled valve or other means after signal is provided either manually or by automatic gauge control before screw travel but after signal has been given for screw travel.

For the purpose of the present invention an initial desired or referenced roll force is determined by a conventional automatic gauge control system, and the changes in the applied roll force relative to this reference roll force will be considered to be a AB control signal. A typical reference roll force signal could be calculated by a screwdown controlling computer as desired for the next pass of the work strip through a particular stand of the rolling mill, and the changes away from the reference roll force that are effected throughout the length of the work strip as it passes through the mill stand .would be sensed and utilized to provide the incremental AB Control Signal,

on either a continuous basis orsome predetermined incre: mental basis. Also, it is assumed here that at reference roll force B, there should be no requirement for a bending force C and for this reason the bending force C will be zero at reference roll force conditions, at least at the initially intended crown condition of the roll. It should be realized that for efforts to extend the effective crown range of any given roll, the reference roll'force B will vary. Thus, a AC signal starting from a zero value for the C signal, is the same as the actual C signal itself. Substituting AB for B in Equation 4 results in an equation as follows: (7) AB=C 1+%)=CK for a desired automatic roll bending compensation, the above equation shows that a fixed ratio of the relationship between AB to C must be maintained.

In FIG. 3 there is illustrated one control concept of the present invention, wherein the upper roll 10 and the lower roll 12 are operative with the workpiece 14 and a screwdown mechanism 16 applies the force B through a roll force sensing device 18 to effect the desired reduction in the workpiece 14. Suitable shape control apparatus 20 is operative to sense the roll force signal provided by the inductive device 18 for controlling the bending shape of the rolls 10 and 12 as will be later described. A force device 22 such as a hydraulic fluid cylinder apparatus or electric motor driven screw mechanism, is operative to supply the bending force C through a force sensing device 24 to the outer end of the neck 26 of the work roll 10 and to the outer end of the neck 28 of the work roll 12. The bending force C applied by the force device 22 is sensed by the force sensing device 24 and a suitable signal is applied to the shape control apparatus 20. The forces B and C applied to the Work roll 10 are compared by the shape oontrol apparatus 20 and a suitable control signal is thereby supplied to a force control device 30 for determining the operation of the force device 22 in opposition to the screw mechanism 16. The roll force signal provided by the force sensing device 18 is applied through a compensation circuit 21 to a conventional roll force gauge control 23, with the compensation circuit 21 being responsive to a control signal from the shape control apparatus 22 for determining the operation of the compensation circuit 21 as will be later described.

In FIG. 4 there is shown a curve illustrating the operation of a typical prior art roll force automatic strip thickness control system. An equation can be drawn forthe well-known straight deformation line as follows:

where h equals the delivery gauge or thickness of the rolled workpiece strip, S equals the separation of the rolls when the mill is empty, F equals the roll force and M is the mill spring constant. The curve 50 represents the front end of the stripand the curve 52 represents the tail end of the strip, Where the tail end of the strip. is colder and harder. It can be seen that moving the screw mechanisms a small amount is required. to produce a higher rollv force as required to give the same output thickness at the tail end of the strip as for the front end of the strip. Y

The curve of FIG. 5 illustrates the changed operating conditions when the roll bending control is utilized in accordance with the teachings of the above referenced copending patent application. It can be seen that forces B and A in this context appear after roll bending control is employed. Since, in the roll bending region only a portion of the screwdown force B appears on the strip to effect reduction, the housing deformation line as seen by the strip suddenly assumes a smaller slope so that considerably more travel of the screws is required to pr'oducethe same gauge correction as before. The present invention takesinto account this. change in slope so that the automatic gauge control system can still function as desired.

There is required in the control system a gompensation circuit for rnultiplying the force..B by a factor to give the new slope as shown in FIGS.

Reviewing the basic expressions:

s B=A+C s 2AB=VA+2C (9) i 4 B A+gA 2AB=A+ A 10 t b. 10 b (11) B24 (11) 211B=A -(ml (m AB The required compensation factor then is seen to be the generalized quantity In the above referenced copending patent application it was shown that regulating force C equal to the ratio relationship would result in correction for roll bending effects. It can be seen that the factor for gauge correction to obtain A in terms of 2B equals one minus the latter ratio obtained and then maintained between C and B previously for roll bending control.

In a hot strip mill automatic gauge control system, an incremental position regulating control is used to move the screw mechanism the correct distance to take out the sensed gauge error. It is proposed in accordance with the present invention to multiply the gauge error signal used to determine the screw movement by to compensate for the lowered slope of the roll force line as applied to the strip.

In FIG. 6 there is shown a right side roll force transducer 60 and a left side roll force transducer 62 connected to a roll force difference circuit 64 for providing a signal in accordance with the difference between the right roll force and the left roll force for the purpose of leveling the roll in the mill. Each of the signals from the respective transducers 60 and 62 are applied to a first control circuit 66 which senses when the right roll force is greater than the left roll force, with suitable circuits to perform this function being well known in this particular art, and which first control circuit 66 when operative applies an output signal to open a gate '68 for then allowing the difference signal from the circuit 64 to be applied to the left screw mechanism 70 for increasing the left roll force as necessary to level the mill. Similarly a control circuit 72 senses when the left roll force is greater than the right roll force and when operative opens the gate 74 for allowing the roll force difference signal to be applied from the circuit 64 to the right screw mechanism 76 for increasing the right screwdown force for the purpose of leveling the mill. The right side bending force transducer 78 and the left side bending force transducer 80 are connected to an average bending force determining circuit 82, which provides an average bending force signal to a bending force difference circuit 84 in conjunction with a reference bending force signal from a circuit 86 for providing a bending force difference or error signal AC to a signal ratio circuit 88. For actual roll force applications in the order of the de signed roll force for the predetermined ground crown shape of a given roll, the reference bending force signal from the circuit 86 would be zero and the signal AC is the same as the signal C.

The output signal from either one of the roll force transducers 60 or 62, with the right roll force transducer 60 being chosen for the purpose of illustration, is supplied through a connection 89 to a roll force thickness error circuit 90 for comparison with the reference roll force signal from a suitable circuit 92 for providing a roll force difference of error signal AB to the signal ratio circuit 88. The control signal from the signal ratio circuit 88 is applied to a control signal source 94 and a bending force control device 96 for applying an appropriate bending force to the rolls 10 and 12 as described in the above referenced copending patent application.

The function of the so far described circuit portions of FIG. 6 is to provide the desired roll crown and workpiece strip shape as delivered from the rolling mill, with the so far described circuit portion being adapted to function to maintain a predetermined and desired ratio for the change in roll force signal relative to the change in roll bending signal by varying the applied bending pressure such that any change in the applied roll force causes a corresponding change in the applied bending force.

A conventional roll force operative automatic strip gauge control system is provided in conjunction with the illustrated bending control apparatus, such that the thickness of the work strip delivered from the mill is maintained substantially constant throughout its length by the provided automatic gauge control equipment, and in conjunction there is additionally provided a shape or profile control through the operation of the so far described circuit portion illustrated in FIG. 6 such that any differences in the applied roll force between left and right ends of the work rolls is initially corrected through the roll leveling control shown in FIG. 6 and then additionally the gauge control apparatus applies the required changes in the roll force to compensate by a corrective bending of the rolls for providing the desired delivery workpiece strip shape.

There is shown in FIG. 6 an operational amplifier 98 responsive to the roll force thickness error signal from the circuit 90 for determining the operation of a conventional automatic gauge or screwdown control system 100. Any changes in the operation of the screwdown mechanism motor 102 are sensed through the screw travel feedback circuit 104 for providing a corresponding feedback signal through one of two paths. A first path is provided through a normally open gate circuit 106 responsive to the provision of a bending control signal by the control signal source 94 and is operative such that a screw travel feedback signal normally passes directly to the operational amplifier 98 through the gate 106 when no bending control signal is provided. Upon the provision of a bending control signal by the control signal source 94 to the bending force control circuit 96, the gate 106 is closed such that the screw travel feedback signal from the circuit 104 must now pass through a predetermined bending compensation circuit 108 before being fed to an input of the operational amplifier 98.

In FIG. 7 there is shown in greater detail the bending compensation circuit 108 and the operational amplifier 98 relative to the automatic gauge control or screwdown control circuit 100.

The right roll force transducer 60 and the left roll force transducer 62 supply roll force signals to an average roll force circuit 61, which in turn provides an average roll force signal to the roll force thickness error circuit 90 for comparison with a reference roll force signal from a suitable circuit 92, and any resulting and determined thickness error signal is supplied to one input of an operational amplifier 98 for application to the screwdown control for determining the corrective operation of the screwdown motor 102 The resulting movement of the screwdown motor 102 adjusts the position of potentiom eter arm to provide a corresponding screw travel feedback signal through the operational amplifier 122 to the bending compensation circuit 108 including the gate 106. When a bending control signal is applied by the control signal source 94 this causes the gate 106 to not be conductive. It being realized that the gate 106 could be a normally closed relay or a suitable switching device which has a normal low impedance path, and upon receipt of the bending control signal from the control signal source 94 is opened and thereby assumes a very high impedance condition to be not conductive. Thus, the screw travel feedback signal from the operational amplifier 122 is now caused, with the gate 106 open and not conductive, to pass through the bending compensation circuit 108 which includes a predetermined set potentiometer eenrgized by a reference voltage source 110 for providing a predetermined ratio compensation to the screw travel feedback signal. The parameters of the potentiometer 112 in combination with the voltage source 110 and the setting position of the potentiometer arm are such that a desired compensation factor is introduced into the screw travel feedback signal such that an additional travel of the screwdown motor 102 is required to balance the roll force signal and desired strip correction.

In the operation of the automatic gauge control portion of the circuit shown in FIG. 7, the roll force error signal from the roll force thickness error circuit 90 is an incremental memory of the change in required roll force B produced by a change in the hardness of the workpiece strip. This produces a movement of the screwdown motor 102 and this screw movement produces a voltage on the output of the operational amplifier 122 proportional to screw travel. The system is so scaled that this movement will produce enough additional roll force to correct the output strip guage to the desired reference value. When the roll bending control system requires a bending force C then the gate 106 will open to insert the ratio compensation factor into the circuit path of the screw travel feedback signal from the operational amplifier 122, thereby reducing the effective feedback value of the screw travel feedback signal supplied to an input of the operational amplifier 98 and causing the screwdown control 100 to provide a greater actual travel of the screwdown motor 102 to balance the roll force error or correction signal from the roll force thickness error circuit 90.

Although the present invention has been described with a certain degree of particularity, it should be understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the scope and spirit of the present invention.

I claim as my invention:

1.'In apparatus for controlling the thickness of a work piece strip passing between the rolls of a rolling mill, the combination of first force sensing means positioned relative to said rolling mill to sense a first force between said rolls relative to a central portion of said strip for providing a first control signal in accordance with said first force, second force sensing means positioned relative to said rolling mill to sense a second force between said rolls relative to an edge portion of said strip for providing a second control signal in accordance with said second force, roll shape control means responsive to said first and said second control signals for applying a roll shape correction force to at least one of said rolls in accordance with a predetermined comparison of said first and second control signals, strip thickness sensing means operative with said rolling mill for providing a thickness error signal relative to a desired strip thickness, and strip thickness control means being operative with said roll shape correction force and responsive to said error signal for controlling the thickness of said strip in accordance with said error signal.

2. The apparatus of claim 1 for controlling the thickness of a workpiece strip passing between the rolls of a rolling mill, With said strip thickness control means being operative with said roll shape correction force for controlling a predetermined response to said error signal for controlling the the thickness of said strip in accordance with said error signal.

3. The apparatus of claim 1 for controlling the thickness of a workpiece strip passing between the rolls of a rolling mill, with said first force sensing means being sensitive to a first force in effect provided between said rolls relative to a central portion of said strip for providing a first control signal in accordance with said first force, and with said strip thickness control means being responsive to a predetermined factor of said error signal when said roll shape correction force is present, with said predetermined factor being related to the distance between said first force and said second force and the distance between said second force and said roll shape correction force.

4. The apparatus of claim 1 for controlling the thickness of a workpiece strip passing between the rolls of a rolling mill including a screwdown mechanism, with said first force sensing means being operative to sense a first force between said rolls at a first location relative to a central portion of said strip, with said second force sensing means being operative to sense a second force provided between said rolls by said screwdown mechanism and relative to an edge portion of said strip, with said roll shape control means applying a work roll shape correction third force to at least one of said rolls external to said second force, and with said strip thickness control means being responsive to said roll shape correction force for being operative with a predetermined factor of said error signal, with said predetermined factor being a ratio of a first distance between the first force and the second force and a second distance between the second force and the third force.

References Cited Plaisted 72- 8 CHARLES W. LANHAM, Primary Examiner. A. RUDERMAN, Assistant Examiner. V 

